When people try to carry out two activities at the same time, their performance may suffer in a number of different ways. By understanding this interference we hope to better understand the functional architecture of the mind/brain. Our research has analyzed dual-task interference in a much more fine-grained way than was the case in previous research. To do this, we have used manipulations targeted to prolong specific mental processes, new ways of analyzing the relationship between performance in each task, and other tools. The results from studies of simple tasks demonstrate several independent forms of dual- task interference, including queuing of response selection ("central" interference) and perceptual capacity limitations; furthermore, they provide hints about the possible neural basis of the queuing. The results challenge the widespread assumption that central processing resources can be shared in a graded fashion. Stringent new tests are proposed to determine whether graded sharing can occur when people are given incentives to favor such sharing. The next two sections of the proposal describe experiments to apply these fine-grained ways of analyzing dual- task interference to "higher cognitive functions" previous analyses in this area have been very sketchy. Experiments are proposed to assess whether time-consuming memory-retrieval tasks can be carried out simultaneously, to determine whether the response-selection queuing apparent in single tasks reflects a general cognitive limitation. The role of attentional limitations in language processing will be explored with experiments combining sentence comprehension and production with serial reaction-time tasks that are designed to continuously occupy central processing machinery. Finally the role of attention in the perception of time will be explored with new designs combining perception and production of temporal intervals with concurrent tasks.